Having sex for anything but love, and/or devotion, is equal to prostitution. Some prostitutes are paid in money, some in promises, some for support, etc. but none are paid for love. Joseph Smith's teenage wives may or may not have been in love with him, but they were told that he could save them and their families for sexual favors. Plural marriage was illegal in the U.S. so it wouldn't made any difference if he was married to them or not. What girl would want to take the chance that because of her, her family might not be saved. Teenage brains are different than adult brains.
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